Experimental Physics and
Industrial Control System

"Liyu, Andrei" <[email protected]> · Thu, 20 Oct 2005 09:24:41 -0400

I had the problem with dbr_size[]. If I am not mistaken you need to use
Multitheading (Project setting -> C/C++ -> Code Generation -> Use
run-time library in VC++ or /MTd /MT options).
Also you can search in tech-talk. I remember this question.

Have a nice day, Andrei.

-----Original Message-----
From: Mark Davis [mailto:[email protected]] 
Sent: Thursday, October 20, 2005 9:06 AM
To: Jens Eden; Williams Jr, Ernest L.
Cc: [email protected]
Subject: Re: Qt-compatible Channel Access lib

First off, thank you Jens for your feedback.  Exactly what I needed to
make 
some progress.

A quick update and another question:

For the moment I simply modified the shareLib.h file to define 
epicsShareFunc as "__stdcall" when compiling Qt applications (I am still

using the MinGWwin32 compiler).  So far everything works fine with the
ca 
and Com lib calls.  Currently using the following functions without 
(apparent) problems:

  ca_context_create()  (without preemptive callback's)
  ca_add_event()  (with callback)
  ca_create_channel()   (with callback)
  ca_poll()   (aka ca_pend_io - so the non-preemptive callbacks can
happen)
  ca_puser()
  ca_clear_channel()
  ca_context_destroy()

Nothing too fancy yet - just setting up a connection and getting
callbacks 
when the value of a PV changes.  I haven't tried using preemptive
callback 
yet.  Perhaps after I get everything else working the way I want
(although 
if anything is going to cause problems, I expect allowing preemptive 
callbacks to be it).

My current problem (and I know this is a "newbie" sort of question, but
I 
haven't had to deal with these kinds of details since the early days of 
windows) is how to similarly modify the epicsShareExtern macro so that 
references to things like dbr_size[] are resolved at link time.  Just
having 
it be "extern" works fine for compiling, but it always shows up as an 
undefined reference when I link.  The same code (and linking with the
same 
libraries) works find on Linux and MacOS/Darwin, so I am assuming it is
just 
a case of the right magic word(s) for the Windows compile/link.

Any ideas?

----- Original Message ----- 
From: "Jens Eden" <[email protected]>
To: "Ernest L. Williams Jr." <[email protected]>
Cc: <[email protected]>
Sent: Tuesday, October 11, 2005 12:44 PM
Subject: Re: Qt-compatible Channel Access lib

> Ernest L. Williams Jr. wrote:
>> On Tue, 2005-10-11 at 16:25 +0200, Jens Eden wrote:
>>>Mark,
>>>
>>>it is possible to link applications compiled with MinGW to
>>>dll-Files compiled with MS Visual Studio.
>>>So in theory it is possible to link your MinGW/QT-Application to
Epics
>>>base compiled with MS Visual C++.
>> No it is not.  We have already gone down this path.  We are dealing
with
>> C++ code and the compiler that you use for building EPICS BASE must
be
>> the same when working with Qt.
>>
>> We built EPICS BASE with MS C++ and tried to link EPICS libraries
with
>> the GPLd version of Qt which uses MinGW only; did not work.
>
> It works for me, attached is a small code snippet
> (it's just a quick and very dirty hack, to show linking and running
> ca_array_get() returns ECA_GETFAIL)
> which you can compile with the following command (make sure MinGW is
in 
> your Path):
> g++ -o ca-test.exe ca-test.cpp
D:\epics\base-3.14.5\lib\win32-x86\ca.lib
>
> You need the EPICS-dlls in your Path to run it.
>
> That's all I tried, so I don't know, if there are other issues with
the
> two compilers if developing real world applications.
>
> Did you try to compile the GPLed version of Qt with MS C++?
>
> Jens
>
> *****************
> #include <stdio.h>
>
> #ifdef __cplusplus
> extern "C" {
> #endif
> __stdcall int ca_context_create(int);
> __stdcall int ca_create_channel(char *, void *, void *, int, void *);
> __stdcall int ca_array_get( long, long, void *, void *);
> __stdcall int ca_pend_io( double);
> __stdcall int ca_flush_io();
> #ifdef __cplusplus
> }
> #endif
>
> # define DBR_DOUBLE 6
>
> int main(void)
> {
>     int result;
>     char *pvname="ringCurrent1";
>     char somespace[500];
>     void *mychid;
>     double doubledata=1.234;
>
>     mychid = (void *)somespace;
>
>     result = ca_context_create(0);
>     if (result != 1) {
>         printf("CA error (%d) ca_context_create \n", result);
> return 1;
>     }
>     result = ca_create_channel(pvname, NULL, NULL, 0, mychid);
>     if (result != 1) {
>         printf("CA error (%d) ca_create_channel \n", result);
> return 1;
>     }
>     result = ca_flush_io();
>     if (result != 1) {
>         printf("CA error (%d) ca_pend_io \n", result);
> return 1;
>     }
>     result = ca_pend_io(1.0);
>     if (result != 1) {
>         printf("CA error (%d) ca_pend_io \n", result);
> return 1;
>     }
>     result = ca_array_get(DBR_DOUBLE, 0, mychid, &doubledata);
>     if (result != 1) {
>         printf("CA error (%d) ca_array_get \n", result);
> // return 1;
>     }
>      result = ca_pend_io(1.0);
>     if (result != 1) {
>         printf("CA error (%d) ca_pend_io \n", result);
> return 1;
>     }
>
>     printf("value: %9.5g\n", doubledata);
> }
>
>
>
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System